1. Field of the Invention
This invention relates to fluid heaters and more particularly to fluid heaters used in connection with high solids materials used in coating applications.
2. Description of Prior Heaters
Fluid heaters for heating coating material prior to application are known. U.S. Pat. No. 3,835,294-Krohn et al. and U.S. Pat. No. 4,199,679-Sharpless describe typical fluid heaters which are cylindrical and have a single spiral passageway through which coating material flows from an inlet at the bottom to an outlet at the top. Heat is transferred from a core or source to the fluid through the passageway sidewalls. Another form of single passageway heater is that shown in German Offenlegungsschrift No. 2156029 published on May 17, 1973. The heater has a series of parallel annular channels formed in a core about a central axis. Fluid to be heated flows from annular channel to annular channel by a port formed in each. Each adjacent port is disposed 180.degree. from the previous port.
In use, the known heaters are not suitable for heat-highly viscous materials such as high solids coating materials which are typically over 50% solids material by weight or by volume in solution/suspension. The high solids coating materials suffer a notable pressure drop when passing through heaters of the type described above, and are not heated quickly, thoroughly or evenly. Increased pumping capacity may be required to attain only acceptable results at a notable increase in cost. Use of a wide passage heater such as the NH-4 wide passage heater manufactured by Nordson Corporation of Amherst, Ohio provides for reduced pressure drop but does not heat the highly viscous material uniformly and provide for sufficient heat transfer.
A heater which heats highly viscous materials such as high solids coating materials with less pressure drop while thoroughly and evenly heating the material is not known.